1. Field of the Invention
This invention relates to temperature control systems which maintain the temperature of an electronic device near a given set point temperature(s) while the device is being operated or tested. Two specific examples of electronic devices which need to be operated or tested at a constant temperature are packaged integrated chips and unpackaged bare chips.
2. Description of the Related Art
Maintaining the chip temperature near a given set point is not difficult if the power dissipation of the chip is constant or varies in a small range while operating or testing. In such cases, it is only necessary to couple the chip through a fixed thermal resistance to a thermal mass which is at a fixed temperature. But if the instantaneous power dissipation of the chip varies up and down in a wide range while operating or testing, then maintaining the chip temperature near a constant set point is very difficult. When chips are being debugged or tested, it is advantageous to evaluate their performance at a variety of temperatures, ranging from cold to hot. Combining the ability to force temperature across a wide temperature range, while accommodating the temperature changes associated with varying instantaneous power dissipation, is very challenging.
Typical approaches to solve this problem involve forced air convection systems that extend well beyond the desired forcing temperature range at both the hot and cold ends. In this way, an attempt can be made to accelerate the chip's temperature conditioning by overcooling or overheating. As the nominal power density of the chips continue to increase, the ability of forced air convection systems to overcool reaches practical limits, causing increases in the temperature error between the desired and actual temperatures relative to set point. Another problem is that chips fabricated in the latest processes have an increased sensitivity to high temperatures. The potential for chip damage due to overheating adds risk to the use of the overheating approach. Increased time to set point is the result, with lost utilization of expensive test equipment and engineering personnel as an expense.
Another approach is the use of dual liquid conduction systems, with one hot and one cold liquid. The proportion of the liquids are mechanically metered to affect the desired forcing temperature. To achieve fast response times, this approach requires that the metering occur very close to the chip. This imposes mechanical packaging constraints which limit the flexibility to bring the surface of the temperature forcing system control surface into contact with the chip or chip package. Even so, the mechanical metering of the dual liquids is much slower to affect a change in the forcing temperature when compared to the temperature changes induced by the chip's instantaneous power dissipation. This also causes increased error between the desired and actual temperatures.
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set out above.